Although it is accepted that human milk is preferable for feeding young infants, comparatively little is known how to optimize lactation and the composition of human milk and what maternal-environmental factors have deleterious effects upon lactation performance, and hence, upon the growth and development of breast-fed infants. Four principal factors which may be important determinants of lactation performance and the quality of human milk have been identified from past studies: ethnic-cultural practices, maternal nutrition, exposure to drugs and toxins, and exposure to natural immunogens. Because of the public health importance of breast-feeding in developing as well as more economically privilege countries and the complexities of the scientific questions which are posed, we propose to organize and conduct an international workshop to facilitate an exchange of scientific data concerning these issues, aid in developing collaborative research regarding human lactation and help the National Institutes of Child Health and Human Development to focus upon the research that should be encouraged in this field. Forty to fifty scientists from the U.S.A., Canada, Mexico, the United Kingdom, Sweden, Guatemala, and Australia will be asked to participate in the conference which would be held in Oaxaca, Mexico between October 2-6, 1985. The workshops are as follows: 1) Ethnic-cultural effects on human lactation, 2) Effect of maternal age and duration of pregnancy and lactation upon human lactation, 3) Lactation performance, 4) Effects of maternal nutrition on human lactation, 5) Drugs and toxins in human milk, and 6) Effect of immunization on the host defense system. The participants will be invited because of their current contributions to our understanding of those questions. Finally, we are requesting to conduct the workshop in Mexico to: 1) gain participation from third world countries in Central and South America, 2) help scientists from developed countries to focus upon problems in third world countries, and 3) provide a relatively inexpensive site for the conference.